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Nominal capacity when full and nominal capacity remaining (from the BMS) do not include the "anti-bricking buffer," which the car will prevent you from entering. However, they do include an "anti-run out of gas" buffer of 3.8 Kwh that is not included in rated miles or SoC% shown on the dashboard. But it can be used (if you're feeling lucky.) See this (old) post for my evidence. Last time I checked, the BMS doesn't have a "usable capacity" variable. It must be calculated.

I think the brick protection is different for each battery size, correct?

And not disagreeing yet, but what proof do we have that the BMS is not tracking brick protection (0% on the dash = 0% usable as of the more recent firmwares)? Can @wk057 verify that? I seem to recall hearing that if you can drive past zero, it just means that some of the modules were out of balance and that nothing below 0% could be expected or counted on.
 
The "proof" is that I did the experiment I linked to yesterday more than once. In fact, on about half a dozen occasions over several months, I got results more or less the same. Each time, I pulled between 3 and 4 kWh out of the battery after the dashboard said zero remaining rated miles. There are no occasions where I failed to get at least 3 kWh and I never had a shutdown, though I think I came close a couple of times. To me that does not seem like modules out of balance. That seems like intentional design. I assume @wk057 would not verify this idea; I fact, I expect he would still dispute it. See this post for more about this if you are interested.


I have about a 2 million row CSV file I'm working on right now that tracks and entire discharge cycle from 100% to 5%.

What software did you use to collect all that data? I use TM-Spy to record CANBus messages and a spreadsheet to analyze them.


By the way, you need to redo those two graphs you just published. Your x-axis (SoC% I assume) is not proportional across its entire length. For example, the horizonal distance between 100 and 90 is larger than the one between 50 and 40. The distance between 10 and 0 is largest of all. If they were all the same, I think a single trend line would fit the curve much better and the stairsteps would not be required.
 
@supratachophobia I entered your numbers. I made a few assumptions based on the numbers and formatting of your sheet.
I'm guessing you got readings for SOC %, "usable" kWh, and RM from the car.
I'm also guessing you calculated "Nominal" either by adding 4 kWh to the 74.7 kWh reported, or multiplying 290 Wh/m by 272 miles, coming up with about 78.9 kWh. I suspect the former since your chart starts at 78.7.
In my 2013 S85, about 286 Wh/m matches rated miles with actual miles.

I suggest that your car is calculating RM by the usable capacity, (74.7 kWh / 272 miles), so is probably using 275 Wh/m for RM calculations.

The left 3 columns I typed in from your post in the 90% thread; which I didn't want to clutter more with this.
The heading of the 5th column is the formula C2/B2 (74.7 kWh / 272 miles), which rounded is 0.2746.
The 4th column is column "C" / .290, yielding the numbers in your EPA column.
The next column is column "C" / 0.2746, yielding very similar numbers to the RM.
The last column is the difference between RM and miles calculated on 0.2746 kWh/m.

upload_2018-7-20_14-24-4.png


I believe a 1 mile difference should be considered within a margin of error, especially since the car is reporting RM in rounded miles. There are a few entries over 1, but I think the car is calculating very consistently.
 
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@supratachophobia I entered your numbers. I made a few assumptions based on the numbers and formatting of your sheet.
I'm guessing you got readings for SOC %, "usable" kWh, and RM from the car.
I'm also guessing you calculated "Nominal" either by adding 4 kWh to the 74.7 kWh reported, or multiplying 290 Wh/m by 272 miles, coming up with about 78.9 kWh. I suspect the former since your chart starts at 78.7.
In my 2013 S85, about 286 Wh/m matches rated miles with actual miles.

I suggest that your car is calculating RM by the usable capacity, (74.7 kWh / 272 miles), so is probably using 275 Wh/m for RM calculations.

The left 3 columns I typed in from your post in the 90% thread; which I didn't want to clutter more with this.
The heading of the 5th column is the formula C2/B2 (74.7 kWh / 272 miles), which rounded is 0.2746.
The 4th column is column "C" / .290, yielding the numbers in your EPA column.
The next column is column "C" / 0.2746, yielding very similar numbers to the RM.
The last column is the difference between RM and miles calculated on 0.2746 kWh/m.

View attachment 318422

I believe a 1 mile difference should be considered within a margin of error, especially since the car is reporting RM in rounded miles. There are a few entries over 1, but I think the car is calculating very consistently.

I'm not sure what you are getting at, but I really do appreciate the help. Are you saying from your interpretation of the data, that Tesla is using 275 wh/m to do the range remaining calculation? How would you explain the near perfect nominal divided by 290 yielding range remaining near perfectly, but only down to around 80%? I see it making sense if they changed the consumption calculation to something other than 290, but isn't the whole point of range remaining to give you a "if you consume this much, you can drive this far" estimation?
 
The "proof" is that I did the experiment I linked to yesterday more than once. In fact, on about half a dozen occasions over several months, I got results more or less the same. Each time, I pulled between 3 and 4 kWh out of the battery after the dashboard said zero remaining rated miles. There are no occasions where I failed to get at least 3 kWh and I never had a shutdown, though I think I came close a couple of times. To me that does not seem like modules out of balance. That seems like intentional design. I assume @wk057 would not verify this idea; I fact, I expect he would still dispute it. See this post for more about this if you are interested.




What software did you use to collect all that data? I use TM-Spy to record CANBus messages and a spreadsheet to analyze them.


By the way, you need to redo those two graphs you just published. Your x-axis (SoC% I assume) is not proportional across its entire length. For example, the horizonal distance between 100 and 90 is larger than the one between 50 and 40. The distance between 10 and 0 is largest of all. If they were all the same, I think a single trend line would fit the curve much better and the stairsteps would not be required.
Wait, are you using a 75kwh battery? My data is only from a 90kwh battery. I don't think their is anything wrong with the 75's....
 
I'm not sure what you are getting at, but I really do appreciate the help. Are you saying from your interpretation of the data, that Tesla is using 275 wh/m to do the range remaining calculation? How would you explain the near perfect nominal divided by 290 yielding range remaining near perfectly, but only down to around 80%? I see it making sense if they changed the consumption calculation to something other than 290, but isn't the whole point of range remaining to give you a "if you consume this much, you can drive this far" estimation?
Your car is using usable capacity to calculate rated miles, just the same as other cars. The reason it appears to track nominal at the beginning is because the delta between nominal and usable % is very small until you get below 80% as the graph below shows.

upload_2018-7-21_23-26-40.png
 
Great thread. This is type of thread I’ve missed here on TMC.

Really interesting findings and I completely understand that it makes sense for Tesla to get the attention away from 90s more than average degradation. We wouldn’t be able to get a reply from Tesla on this as they just want us to be uneducated on things like this. People we would be in contact with already are less informed on batteries than most of us. So all of these will remain a speculation almost always.

However the capacity in Ah instead of kWh theory is brilliant. If true we would feel bad about putting Tesla in the spot for this unofficial ‘finding’. I want to know what @wk057 would have to say about that counter theory.

I wouldn’t be able to add anything new as my knowledge of batteries don’t extend all the way out here. There are just so many variables you wouldn’t be able to get a precise reading on a source of chemical energy anyway. How does the BMS report a certain kWh in the start anyways? Which nominal voltage is multiplied with which Ah? If BMS isn’t reporting Ah at all, is it really the real BMS? We need more battery people in here.
 
I'm not sure what you are getting at, but I really do appreciate the help. Are you saying from your interpretation of the data, that Tesla is using 275 wh/m to do the range remaining calculation? How would you explain the near perfect nominal divided by 290 yielding range remaining near perfectly, but only down to around 80%? I see it making sense if they changed the consumption calculation to something other than 290, but isn't the whole point of range remaining to give you a "if you consume this much, you can drive this far" estimation?
I'm just showing that the range indicator is changing linearly with energy use.
And it does appear to me that your car is using 275 Wh/m. The only way I think you can be sure is to try to match miles driven with the range indicator's change; with no stops. Like I said, mine syncs up at about 286.
 
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This thread really sparked up an interest in me so I got into searching/thinking. Here's my speculation about what's happening;

DISCLAIMER: I'm not an engineer or a technician. Everything I know about EVs and batteries I learned online reading vigirously about this very exciting technology.

First I'll sum up what I understood so far;
- OP, @supratachophobia has a Model S 90D. He also monitors his car's Canbus messages using a fan-made software likeTM-Spy to spy on his BMS values. He claims that his car is showing rated miles on his dash by dividing the rated mile consumption figure (revealed by @wk057 in his amazing work) by the nominal capacity his pack reports. (including the alleged 4kWh buffer) However his observations suggest this Rated Miles = nominal capacity / RM efficiency formula changes as the battery SoC gets lower. So much so that he loses 4-6% at the bottom 20% of his charge.
- wk057 supports this idea and suggests this just might be Tesla's way of trying to hide more than average degredation of the original 90 packs. As we all remember original 90s lost a lot of rated miles quickly when they first started delivery. Then their supercharging C-rates dropped, then maybe this update was pushed hiding the lost rated miles by absorbing the degradation inside the entire discharge. To make things more worrying he shared his working theory that in virtually all cars including the Model 3, consumption figures are shown less in the first half of the discharge, more at the second half.

Here's how I think before we jump the gun on Tesla.

Batteries are not a pint, a jug or a litre. What you get out of it depends on A LOT of different factors that are hard - if not impossibl - to replicate do the decimal every single time. So SoC determination is always a guess. We are reading from the cars' Canbus that they have xx kWh of energy in them. We don't know how that energy figure was derived. Basic math suggest that for the 90 pack every cell is 3,3Ah at 3.7V nominal and there is a 74P96S setup which results in 86,7kWh nominal. However in reality battery capacity is the total area under the discharge voltage curve, which changes a lot on every situation. So nominal values just give us a ballpark idea.

Also, voltage range is determined by Tesla, not the battery itself. For Tesla's case 4.2V = full and 3.0V = empty. So as you can see from the graph below (I know it isn't accurate, just to give an idea) assuming a linear nominal voltage x amp hour = capacity formula is wrong. When you consider the discharge period and assume linearity it could be that it is understated in the first half and overstated in the second. Because I think the way 'consumption' is showed is just the delta SoC divided by distance traveled repeated every n time period. Which could explain the variance in consumption figures depending on SoC @wk057. (sorry for the terrible drawing)

HvUQNFmT.png


However I refuse to believe Tesla would just report kWh capacity in their BMS by just multiplying nominal voltage with rated amp hour capacity. So I got into searching how fuel gauging is done in batteries. Gotta say it is much more complex than I expected. Here's what I got so far;
There isn't a single true method. There are multiple methods and a combination of them is used. We don't know which Tesla uses but in general;
1) Book keeping. Also called coloumb counting. Manufacturer knows the rated ideal capacity of the battery when full and tells it to BMS at the beginning. Starting from the first cycle BMS counts the coloumbs going in and out, keeping the books to report how much 'should be' in the pack.

However this can be full of errors over time so an adjustment method is also there so;

2) Impedence and open circuit voltage measurement: Battery's voltages wouldn't say much about the SoC under load however when contactors are open - hence pack is in open voltage state - battery's impedence, voltage and temperature inputs would give us an accurate reading of SoC and SoH. There are very complex and proprietary algorithms about this but everytime we put the car in 'P' and leave, SoC is adjusted.

So my theory is that Tesla reports the rated miles on the dash using columb counter's figure when full. However as it is depleted other methods are used to adjust the remaining capacity more accurately so rated miles figure is also adjusted. It could also be that the Canbus message of remaining kWh nominal/usable we decoded is what the coloumb counter is reporting only. AFAIK UI SoC and Canbus SoC doesn't match up completely. When UI says 0%, can bus can still report some usable kWh. So expecting the BMS Canbus kWh figure to always be right to the decimal about rated miles figure could be wrong because of this @supratachophobia.

However Tesla isn't off the hook just yet because even if they are reporting RM when full using coloumb counter's figures, they shouldn't be using nominal, they should be using usable. My theory explains the anomalies and non linearity we see during discharge but Tesla indeed could be hiding the more than average degredation for early 90s just by changing a line of code for the high SoC rated miles displayed.

Really interested to hear what you guys think. Please correct me if I'm wrong as everything I learned, I learned online.
 
Your car is using usable capacity to calculate rated miles, just the same as other cars. The reason it appears to track nominal at the beginning is because the delta between nominal and usable % is very small until you get below 80% as the graph below shows.

View attachment 318915
It's not using usable capacity to track rated miles at 100% though. If you try to use the 275 wh/mile number, it would only fit the equation after you drop below 80%. The changeover from nominal to usable using 290 wh/mile is the only, and simplest, number you can plug in and get the *exact* numbers you see on the dash. I have another log file to graph, I think we'll get some more precise info from it so we can continue the discussion. I *absolutely* appreciate the counter-points offered here. This is "hacking" at it's finest, trying to figure out what the car is doing behind the scenes.
 
As promised, I have a graph for a 100% to 1% trip on a 90kwh battery, for single long contiguous trip. The red line is the depletion of the battery if Nominal Capacity is used to calculate Remaining Range for the entire trip (which matches what the car reports as starting with). The yellow/orange line is the depletion of the battery if Usable Capacity is used to calculate Remaining Range for the entire trip (which matches what the car reports as ending with).

The black line is the ACTUAL Range remaining as reported by the car, for the entire trip.

So, yes, a million lines of data proves that the car is changing what it is using to calculate Range Remaining. And it's changing between Nominal and Usable. The result is that the driver is informed of more available range than he/she actually has available at 100%, with the true remaining range only to be shown only less than 20% and most accurately at 10%.

Source data freely available to @ran349, @emir-t , @Brass Guy, @wk057, or anyone else that would like to pick apart the numbers and see if different conclusion can be drawn. But my conclusion is that Tesla is lying to 90kwh owners about the actual degradation to their batteries.....


BatteryData.jpg
 
The black curve doesn't surprise me. I have seen a similar behavior on my 85 pack. When full the true SoC is 100% and the car reports 100%. As I'm trying the percentages drift apart more and more. When the car shows 0% battery the true SoC is actually 4-5%. That translates exactly to the black curve in your graph.

My theory is (and please correct me if I'm wrong) is that the rated range is not calculated based on the usable capacity but down to where the car shuts down. When Tesla did their EPA testing I guess they calculated driving the battery down to zero using the bricking buffer. Technically it's not incorrect because that's the true battery capacity, but it's still cheating as the last 4 kWh are not available to owners. Sometimes the car let's you go a little beyond 0% but that's a different topic.

Anyways, back to my original comment, the behavior of having true 100% at the beginning but 0% rated range at 5% true SoC is definitely happening in my 85 as well.

bufferSm.jpg
 
The black curve doesn't surprise me. I have seen a similar behavior on my 85 pack. When full the true SoC is 100% and the car reports 100%. As I'm trying the percentages drift apart more and more. When the car shows 0% battery the true SoC is actually 4-5%. That translates exactly to the black curve in your graph.

My theory is (and please correct me if I'm wrong) is that the rated range is not calculated based on the usable capacity but down to where the car shuts down. When Tesla did their EPA testing I guess they calculated driving the battery down to zero using the bricking buffer. Technically it's not incorrect because that's the true battery capacity, but it's still cheating as the last 4 kWh are not available to owners. Sometimes the car let's you go a little beyond 0% but that's a different topic.

Anyways, back to my original comment, the behavior of having true 100% at the beginning but 0% rated range at 5% true SoC is definitely happening in my 85 as well.

View attachment 323024
It looks like it's using Nominal Remaining as your SOC reading from the app maybe?

Edit: And you know what? If the car actually stuck with Nominal the whole way, our 0% would actually be pretty dangerous because more of us would be risking damage by taking it to the limit at times. However, if the were staying with Usable the whole way, we'd be up in arms because we'd know the truth, that 40 miles of degradation in 2 years is pretty extreme and doesn't speak well of the 90kwh chemistry. So I imagine that from Tesla's viewpoint, they were in a tough position. So they figured they could get away with performing a little math voodoo and no one would be the wiser.
 
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I still don't see any "funny business." The black line looks perfectly straight to me, just a different slope - i.e. a different Wh/m than you are assuming.
They way I interpret what you're supposing, the black line should parallel/overlay the orange line at the top, then curve (or bend) toward the yellow, then parallel/overlay the yellow at the bottom.
It still looks linear to me.

I won't say that Tesla never updated the software to calculate based on a different Wh/m though. That would not surprise me.
 
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I still don't see any "funny business." The black line looks perfectly straight to me, just a different slope - i.e. a different Wh/m than you are assuming.
They way I interpret what you're supposing, the black line should parallel/overlay the orange line at the top, then curve (or bend) toward the yellow, then parallel/overlay the yellow at the bottom.
It still looks linear to me.

I won't say that Tesla never updated the software to calculate based on a different Wh/m though. That would not surprise me.
I agree. As @David99 shows, his 85kWh battery does the same thing. if there is any "funny business", it's happening on all other batteries as well. I know it happens on my 70 also.
 
Interesting that 340 watts per mile is the EPA number. And if that's the case, then where can they possibly get the other numbers from?

My hang up is this: Whichever way you slice it, Nominal or Usable, you get two numbers. And only one of those numbers faces the owner; the other is never seen anywhere. Assuming that consumption you listed is right, here are all the variations based on 290 and 340 w/m:

New (based on wk057 research)
85.8 nominal brand new
290 w/m = 294 miles (this was actually advertised, correct?)
340 w/m = 249 miles

81.8 usable brand new
290 w/m = 282 miles (wasn't there some advertising that the 90 was 6% better than the 85kwh?)
340 w/m = 240 miles

Brand New Observed After 1 Month
290 miles
84.1kwh (nominal)
80.1kwh (usable)

Now
78.9 nominal
290 w/m = 272 miles (this is the number I see on the dash)
340 w/m = 232 miles

74.9 usable
290 w/m = 258 miles
340 w/m = 220 miles
Lets be accurate. It is not "340 watts per mile is the EPA number", it is 340 watts hour per mile. Your post shows 290W/m, 340w/m where it should be 290WH/mi and so on.
 
I still don't see any "funny business." The black line looks perfectly straight to me, just a different slope - i.e. a different Wh/m than you are assuming.
They way I interpret what you're supposing, the black line should parallel/overlay the orange line at the top, then curve (or bend) toward the yellow, then parallel/overlay the yellow at the bottom.
It still looks linear to me.

I won't say that Tesla never updated the software to calculate based on a different Wh/m though. That would not surprise me.
I'm saying they need to pick one and stick with it the whole way. I'm not seeing how you are confused on the interpretation of what they have done. They are artificially inflated the starting number on purpose.....
 
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I agree. As @David99 shows, his 85kWh battery does the same thing. if there is any "funny business", it's happening on all other batteries as well. I know it happens on my 70 also.
I bet you lunch your 70 isn't doing the same thing. I bet that according to your BMS, the full rated range divides perfectly into your Usable Capacity number using a single agreed upon watt/hrs per mile for the entire depletion curve.
 
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I'm saying they need to pick one and stick with it the whole way. I'm not seeing how you are confused on the interpretation of what they have done. They are artificially inflated the starting number on purpose.....

What they are showing is a 100% to 0% scale that goes from true full to 5% full (true state of charge). So their calculation is linear and consistent. But I agree it is not correct to show rated range based on the entire capacity of the battery when they don't allow you to use the entire capacity. They are fooling us that way and I think that's not OK. The reason they can get away with it is that they make no statements what energy consumption correlates to 'rated range'. There are also many variables while driving that all affect range so no one can claim they are not getting the promised range. Tesla can always claim all other factors can affect range.

Now I don't think they are trying to hide degradation that way. This behavior has been like that since the car was new.
 
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My car is doing what @David99 is doing, and what yours is doing. If you take your full rated miles and multiply by percent remaining SOC as displayed by your battery on the dash, you will fall exactly on your black curve you plotted above. I did that with your previous data and showed it above in my earlier graph.
 
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